store: Add OidValue to Arrow RecordBatch conversion

Implement rows_to_record_batch() which converts Vec<DynamicRow<OidValue>>
into Arrow RecordBatch objects. Uses a type-erased ColumnBuilder enum that
dispatches on Arrow DataType to create the appropriate array builder.

Supports all OidValue scalar variants (Bool, Int, Int8, Bytes, String,
BigDecimal, Timestamp) and all array variants (BoolArray, Ints, Int8Array,
BytesArray, StringArray, BigDecimalArray, TimestampArray). Block range
columns arrive as separate Int32 values from the dump query, keeping the
converter as a clean 1:1 mapping.